1. Field of the Invention
The present invention relates generally to train control and braking systems, and in particular to braking systems and methods of determining a safety factor for use in a braking model or algorithm on an operating train.
2. Description of the Related Art
As is known in the art, trains, which include at least one locomotive and, typically, multiple railcars, employ complex braking systems and arrangements for slow or stopping the train in variety of conditions and environments. For example, existing braking systems are shown and described in U.S. Publication No. 2007/0142984 and U.S. Pat. Nos. 8,019,496; 6,314,358; 5,744,707; 4,562,543; 4,384,695; 4,235,402; 4,005,838; 4,005,837; 3,921,946; and 3,731,193. Further, many train systems and networks use some form of computer-controlled train management system, such as a Positive Train Control (PTC) system (e.g., the I-ETMS® of Wabtec Corporation). These computer-controlled train management systems have on-board computers or controllers that are used to implement certain train control and management actions for ensuring safe and effective operation of the train.
In addition, the computerized braking control system of the train management system uses a braking model or algorithm to build or determine stopping distances as the train advanced through the train network. Such stopping distances are based upon certain specified train-based operating parameters and/or variable feedback from a number of sensor systems and ancillary determinations, e.g., track grade, track curvature, train speed, train weight, brake pipe pressure, braking system reservoir pressures, and the like. Accordingly, the braking model must account for those various parameters, but must also account for variation in the system parameters while providing a stopping distance that has a very low probability of stopping the train past the target location.
As is also known, these stopping distances are used to build a braking profile or curve that estimates or predicts when train will stop, such as at a specified target ahead on the track. This braking profile or curve is continually calculated using the braking model using the changing feedback and variable determinations to provide an updated braking profile or curve ahead of the train. In general, this braking profile or curve may be used to visually illustrate (e.g., to a train operator) where the train is predicted to stop if a full-service penalty brake application is initiated. Again, this braking profile or curve is continually (e.g., 1-3 times per second) updated so that the operator has an ongoing understanding of how and when the train would stop during a penalty brake situation, such as by displaying a predicted braking distance to the operator (e.g., a line on the operator's display that depicts the point where the train will come to a stop).
The braking model or algorithm is developed by executing a multitude of scenarios under a wide variety of conditions and variables related to all aspects of the train and its projected surrounding environment. Once a certain amount of data is collected however, it is recognized that some distributed variability exists for predicting the stopping distance. By varying certain parameters representing the train conditions and/or its environment, a normal distribution is developed. However, and based upon certain rules and/or standards, a safety factor is required to ensure to a specified probability that the required stopping distance will be safely short of the target. Historically, the stopping distance has been modeled as the combination of a nominal stopping distance for a full-service penalty brake application and the safety factor. Further, these existing safety factors are calculated based upon the train speed, and provides the addition to the nominal distance required to fall within the probability of stopping short of the target location. However, these existing speed-based safety factors lead to unreasonably large stopping distances with light trains or uphill grades. Therefore, there is a need in the art for an improved braking system and/or safety factor that minimizes the chance that the train will stop too great of a distance before the target location.
Still further, and during a penalty brake application, the braking model continues to monitor and predict the stopping distance, such as to a specified target location. In particular, this stopping distance would visually illustrate to the operator examining the in-cab display unit whether the train is predicted to stop before, at, or after the target location. While a prediction that the train will stop before or at the target location may not pose a significant safety issue, a predicted stop after the target location could prove problematic or unsafe. Therefore, there is a need in the art for an improved braking system that monitors and implements some action if it is predicted that the train will stop beyond the target location.